test: Add coverage for :is()/:matches()/:where() containing nested :has() selectors and comma-separated lists (#4422)

* Initial plan

* Initial plan

Co-authored-by: matthew-dean <414752+matthew-dean@users.noreply.github.com>

* test: add test cases for :is()/:matches() containing :has() (fixes #4378)

Co-authored-by: matthew-dean <414752+matthew-dean@users.noreply.github.com>

* test: add :where() and comma-separated list test cases for pseudo-selectors

Co-authored-by: matthew-dean <414752+matthew-dean@users.noreply.github.com>

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Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: matthew-dean <414752+matthew-dean@users.noreply.github.com>
Co-authored-by: Matthew Dean <matthew-dean@users.noreply.github.com>

Author: Copilot